Cornuault, Pauline

Research interest

My research focuses on the Palaeoclimate and Palaeoceanography, especially on tropical areas and on time scales from the Miocene to the Pleistocene. I am particularly interested on the studies based on foraminifera and coccoliths, using palaeontological (and geochemical) tools.

PhD Project

Keywords: Coccolithophores; Planktonic Foraminifera; Palaeoproductivity; Warm period; Carbon cycle.

We suspect that the total productivity by biogenic carbonates in ocean is not constant through time. Furthermore, the actual pelagic carbonate production accounts for a large part of ocean biogenic carbonate (more than 50 %) (Milliman, 1993). Today, understanding the marine water column biogeochemical processes is one of the hottest research topics which have to be elucidate (Legendre et al., 2018). More than 95 % of the Carbon present in the sedimentary sink is composed of coccolithophores and planktonic foraminifera (Brummer and van Eijden, 1992). Boudreau et al. (2018) demonstrates that if carbonate productivity changes one time scales of 100 to 106 years, it can affect ocean acidification but also the atmospheric carbon by counter-pump process. They call it the “biological compensation”:

So far, even if some studies (Gupta et al., 2004) demonstrate that the temperature could be considered as the major driver of productivity, we don’t know exactly how pelagic carbonate production changed in the past in response to changes in atmospheric carbon dioxide and warming.

We want to study how pelagic carbonate production responds to these forcing. We want to determine if there is an increase or a decrease of pelagic carbonate production and attempt to estimate the amount of change as a function of forcing in different time scales. Do foraminifera and coccoliths respond differently to climate forcing / at different time scales?

For this study, we chose three different warm periods which are the warmer periods in the recent Earth History. First, we chose the Mid-Miocene climate optimum and the Pliocene Warm Period. For these periods, the main part of variability is driven by orbital cycles. We will analyse the samples on orbital time-scale to quantify the orbital-scale variability in carbonate production. For that, we will study palaeobioproductivity records at high-resolution during a few orbital cycles for cold, intermediate, and warm state of each key period. Secondly, we will study the response of productivity for the Marine Isotope Stage (MIS) 5 and the MIS 11, which are both warm interglacial periods from the Quaternary, and the closer to the warm present Holocene (Loutre and Berger, 2003). For these, we will sample at high resolution on glacial/interglacial time-scale around the termination.

This project is divided in four chapters based on foraminifera and coccoliths studies:

What is the cause of the cyclicity observed in sediments?

Is there a link between warming and morphometry?

Is the change ecological or physiological?

Comparison to other sites / data synthesis / sand fraction and climate warming

In a context of warm climate (and warm ocean), there is an expansion of the productivity zone, and processes controlling the carbon fluxes changes (Olivarez Lyle and Lyle, 2006). There is also a link between the metabolism and the size of pelagic organisms (Boscolo-Galazzo et al., 2018), that influences the atmospheric CO2 and affects the global carbon cycle (Olivarez Lyle and Lyle, 2006). This was also demonstrated by Hoppe et al., (2002) who found higher atmospheric CO2 and dissolved CO2 in seawater. In this context, it’s absolutely necessary to understand the climate system during the past warmer periods than today in order to understand the upcoming changes.

Former research projects

2018 (5 MONTHS) › CEREGE¹› Palaeoceanography: “Coccolithophores’ response to environmental changes at the Plio-Pleistocene transition in the Indo-Pacific Warm-Pool”, under the supervision of Dr. L. Beaufort (research project of the final year of my masters degree).

- Determination and counting of 6 species of Discoaster(manually), counting, determination and evaluation of the calcite mass for 11 species or group of species (using an automated microscope) in order to identify the ocean condition’s variability in the Indo-Pacific Warm-Pool related to the ocean cooling during the Plio-Pleistocene transition and volcanism.

2017 (2 MONTHS) › CEREGE¹› Palaeoceanography: “Coccolithophores’ response to environmental changes at the Plio-Pleistocene transition in the Indo-Pacific Warm-Pool”, under the supervision of Dr. L. Beaufort.

- Preparation of coccoliths slides using a quantitative decantation method.

2017 (2 MONTHS) › CEREGE¹› Palaeoceanography: “Benthic foraminifera and palaeoclimatic and palaeoenvironmental reconstructions: deep ocean response to glacial-interglacial transition in the North Indian Ocean (Bay of Bengal)”, under the supervision of Dr. L. Licari and Dr. T. De Garidel-Thoron (research project of the first year of my masters degree).

- Picking, identification and counting of benthic foraminifera, in order to reconstruct the deep-ocean evolution in the Bay of Bengal during the last Glacial cycle.

2016 (3 MONTHS) › CEREGE¹› Palaeoceanography: “Coccolith-based palaeoclimatic and palaeoenvironmental reconstructions in the North Indian Ocean (Bay of Bengal)”, under the supervision of Dr. C. Bolton.

- Preparation of coccoliths slides, microfiltrations of different size of coccoliths.

- Washing, sieving, picking and identification of benthic foraminifera for geochemical analyses.

2016 (1 MONTHS) › CEREGE¹› “Development of a new relative continental atmospheric humidity marker: ¹⁷O-Excess signature of plant’s water (phytolith based)”, under the supervision of Dr. A. Alexandre (research project of my bachelors degree).

- Preparation of phytoliths slides, determination and counting of different morphotypes, calibration of the 17O-Excess index.

¹Centre européen de recherche et d’enseignement en géosciences de l’environnement

Publications

Alexandre, A., Pauchet, S., Landais, A., Piel, C., Devidal, S., Roy, J., Vallet-Coulomb, C., Sonzogni, C., Couapel, M., Pasturel, M., Cornuault, P., Xin, J., Mazur, J.-C., Prié, F., Bentaleb, I.: Towards a new proxy of continental atmospheric humidity: the triple oxygen isotopic composition of plant biosilica, AGU, December 2016, San Francisco, USA.

Alexandre, A., Landais, A., Vallet-Coulomb, C., Piel, C., Devidal, S., Pauchet, S., Sonzogni, C., Couapel, M., Pasturel, M., Cornuault, P., Xin, J., Mazur, J.-C., Prié, F., Bentaleb, I., Webb, E., Chalié, F. and Roy., J.: The triple oxygen isotope composition of phytoliths as a proxy of continental atmospheric humidity: insights from climate chamber and climate transect calibrations, Biogeosciences.